Apparatus for applying electrostatic developer powder by means of a magnetic brush



March 26, 1957 c J YOUNG 02,786,441

PER

APPARATUS FOR APPLTIN'G ELECTROSTATIC DEVEL POWDER BY MEANS OF AMAGNETIC BRUSH Filed July 20, 1953 2 Sheets-Sheet l @di fj" Z; l IINVENTOR. A id Marla; (fl 5317 f; 43 66 BY .11 TTOR NE 1 March 26, 1957c, J YOUNG 2,786,441

APPARATUS FOR APPLYING ELECTROSTATIC DEVELOPER POWDER BY MEANS OF AMAGNETIC BRUSH 2 Sheets-Sheet 2 Filed July 20, 1953 INVENTOR.

cl Yzzag )1 TTOR NE Y United States Patent Ofice 2,786,441 iatented Mar.26, 1957 APPARATUS FOR APPLYENG ELECTROSTATIC DEVELOPER PGWDER BY MEANSOF A MAG- NETIC BRUSH Charles J. Young, Princeton, N. J., assigncr toRadio Corporation of America, a corporation of Delaware Application July20, 1953, Serim No. 369314 11 Claims. (Cl. lid-51) This inventionrelates to electrostatic printers, and more particularly to a novelmeans for continuously sweeping a brush or brushes composed of filamentsor bristles of a ferromagnetic type of developer mix across the recordreceiving surface of a recording member such, for example, as acontinuously moving sheet or web of paper having a light sensitive orphotoconductive surface.

Light projected through frames of film or drawings on tracing paper willimpose a latent charge image upon the previously charged photoconductivesheet or web of an electrostatic printer. This web is in continuousmotion in printers of the continuously operating type. Pigmentedelectroscopic powder, for example, may be supplied to the web so thatthe charge image can attract the powder coating which maltes it visible.A developer powder mix and method of application using a ferromagneticcarrier is set forth in the copending application for Letters Patent ofthe United States of Harold G. Greig, Serial No. 344,123, filed lvlarch23, 1953.

An improved ferromagnetic brush arrangement having magnet poles aboveand below the photoconductive sheet or web is set forth in the copendingapplication for Letters Patent of the United States of Edward C. Giaimo,In, Serial No. 365,152, filed June 30, l53.

A ferromagnetic brush which drops and reforms its bristles to provideuniform mixing of carrier and developer is set forth in the copendingapplication for Letters Patent of the United States of Edward C. Giaimo,IL, Serial No. 365,151, filed June 30, 1953.

In continuously operating electrophotographic apparatus to achieve rmproduction speed the web must move very rapidly. The method andequipment for applying developer powder must be highly efficient touniformly coat color the image consistently, especially where the web isery wide. Reproduction of large sheets of mechanical drawing is aparticularly demanding type of service.

An object of this invention is to provide a continuously sweeping brashof ferromagnetic developer mix for an electrostatic printer which willhave an even powder distribution bristle formation completely across theentire record receiving surface. A closely related object is to provideplity of spaced moving brushes to perform a similar auction.

Another object of this invention is to provide an improved carrier for aferromagnetic brush which will thoroughly shed and reform its bristles.

Another object of this invention is to provide a developer powderapplicator brush for a continuous electrostatic printer which willprovide even coloration completely across extremely wide webs of paper.

A further object of this invention is to provide a continuously sweepingelectrostatic printer developer brush applicator of the ferromagnetictype which will provide substantially equal flux paths through allpoints of the brush so that bristle formation will be uniformthroughout.

Still another object of the present invention is to pro- 2 videcontinuousl sweeping developer powder applicator brush for a. printer ofthe electrostatic type using ferromagnetic bristles which drop andreform with a renewed supply of electroscopic powder supplying an eventoner to powder ratio providing even coloration completely across amoving web.

A still further object of the present invention is to provide a.developer powder applicator brush of the ferromagnetic type for anelectrostatic printer which will sweep completely across the surface ofthe moving web with bristles of uniform stifiness and size which containa uniform toner to powder ratio giving even streak-free col on of tieimage on the moving web of the photoconductive web.

A still further object of the present invention is to provide aferromagnetic developer powder applicator brush for an electrostaticprinter which will reliably, uniformly, and evenly color the image on aphoto conductive sheet.

In one illustrative embodiment of the present invention, the sheet ofphoto conductive paper bearing the latent charge image passes betweentwo magnets of opposite polarity. One of the magnets is above the sheetand the other of the magnets below the sheet. Two vertically mountedpulleys are mounted in the same plane at the ends of the lower magnets.An endless non-magnetic belt of thin hr 55, paper, or plastic passesaround both these pulleys passes over the top of the lower magnet. Theupper surface of the belt is adjacent the lower surface of the movingphoto-conductive paper. The charge image is inprirted upon this lowersurface. A horizontally rota tray carries a mixture of ferromagneticpowder and toner under and adjacent to these pulleys.

As the belt rotates from a position near the bottom or close to thesurface of this rotating tray it enters the magnetic field between thetwo magnets. It, therefore, picks up bristles of the ferromagneticpowder which triboelectrically hold the toner.

A continuous brush of these ferromagnetic bristles passes across themoving surface of the web upon which the latent charge image is imposed.The higher potential charge image attracts the toner from theferromagnetic bristles. A continuous brush, therefore, sweeps in arelatively narrow path across the entire surface of the paper. As thisendless belt brush passes out of the magnetic field between the upperand lower magnets it drops the mixture of ferromagnetic powder and toneronto the rotating tray once more.

The supply of electroscopic powder or toner on the brush is depletedwhile it is passing across the paper. Toner is added to the mixturewhile the powder is upon the tray. The tray rotates carrying areplenished mixture of toner and ferromagnetic powder to the originatingor picking-up pulley.

To provide even coloration completely across the page, two oppositelydirected belts are used on extremely wide sheets. This insures that theportion of the web on the far side of the first brush stroke, whichmight receive an insufficient supply of toner, will be darkened by thefreshly renewed toner in the second oppositely directed brush.

in the double belt arrange rent the web and belts pass within the gapbetween the ends of two abutting U-shaped magnets. The magnetic lines offlux pass twice through the web and belts in flux paths of uniformlength across the width of the web. This provides a perfectly uniformdistribution of lines of flux across the width of the web. As a resultthe bristles of ferromagnetic powder will therefore be uniform instiffness and size completely across the width of the paper. A uniformpowder coating is, therefore, applied no matter how wide a sheet isused.

Other objects and advantages of the present invention will becomeapparent to one skilled in the art from a reading of the Specificationin conjunction. with the following drau ing'whercinf Figure l is a viewin sectional elev t on of one form of apparatus in accordance with thecation providing a doublebelt continuous sweep developer powderapplicator brush;

Figure 2 is a section in elevation taken through Figure 1 on the line2-2 in thedirection of the arrows;

Figure 3 is a section in elevation taken through Figure 1 on the line3-3 in the direction of the arrows;

Figure 4 is a plan view of another form of apparatus providing a doublebelt continuous sweep developer powder applicator brush; and

Figure 5 is a section in elevation taken through Figure 4 on the line 55in'the direction of the arrows.

In Figures 1, 2, and 3 is illustrated one embodiment of the presentinvention. Reference to these figures will show pole pieces and 11 abovethe photo conductive web or sheet of paper 12. Permanent magnets 15 ofAlnico, for example, join the pole pieces it) and 11.

The structure including the pole pieces 16 and 1% is supported in anysuitable manner, as by brackets 91 secured to any static-nary part 92.Below the web 12 are located pole pieces 17 and 18. Magnets 2! connectthe pole pieces 17 and 1-8. A suitable support such as T shaped pedestal93 extending from the base 42 carries the pole pieces 17 and 13. Thepolarity of magnets 15 and 28 is so directed. that pole pieces 19 and 17will be respectively of opposite polarity and 11 and 13 will also berespectively of opposite polarity.

Extensions 21 and 22 are mounted at the ends of pole pieces 17. Similarextensions (not shown) are provided at the ends of the pole piece 18.Shafts 24 and 25 are fixed within these extensions. These extensions aremade of iron as are the pole pieces.

Iron pulleys 27 and 28 rotate on shafts 24 and 25 respectively. Thecircumference of the pulleys tits closely within the cutout ends of thepole pieces so that the lines of flux in the pole pieces continue acrossthe short gap and through the pulleys and the pulleys are included inthe flux path circuit. An endless flexible belt 3% made of anon-magnetic material through which lines of flux will pass, such, forexample asplastic or brass, is looped around pulleys 27 and 28. Idlerpulleys 31 and 32 on brackets 33 and 34 keep the belt 3% tight on thepulleys.

A similar arrangement of pulleys and a belt 35 provided'for the polepiece 18, one of these pulleys, namely pulley 23, appears. in Figure 3.A pole piece extension 36 is secured to the end of polepiece It? andcarries an adjustable arm 14 on a pivot screw 83. approaches the farside of pulley 27. A similar pole piece extension 37 is secured to theother end of pole piece 11 and its'adjustable arm 84 on pivot screw 36approaches the far side of pulley 23. Brass facing strips 16 and 2d aresecured to the side and ends of arms 14 and 34.

Tray 40 rotating on a centrally located bearing ring 41 is supported onthe base 42, by suitable supports such as the pedestals 8%. A supply offerromagnetic developer. such as finely divided iron mixed withdeveloper powder or toner is carried in depression 43 annularly disposedon tray 40.

In operation, the paper 12 moves continuously through the magnetic fieldin the direction shown.

Lines of flux pass in a closed circuit from the north polarity polepieces through the web into t e south polarity pole: pieces. As the.pulleys rotate, the upward rotating pulleys 27 and 23 pick up or attractmagnetically the ferromagnetic mix in the high flux density gap betweenthe pulleysv 27 and 23 and the arms 14 and 84 respectively. The brassfacing strips 16 and 26 prevent the mixfrom sticking to the iron arms 14and 34.

The coated paper 12. is provided with a distributed electrostatic chargeover one of its surfaces which. is exposed to the influence of an;electrostatic charging device .6; The" charging device may comprise aplurality of The arm 14 fine wires 9-8 carried by a pa of spacedinsulating membe'rs99 only one of the latter appearing in Fig. 2 of thedrawing. It will be understood that the insulating members are spaced insuch a manner that the wires 98 span the width of the paper sheet 12. Itwill be understood that light is preferably excluded during the chargingstep. A source of high voltage D. C. (not shown) is connected to thewires 98 so as to give them a negative charge with respect to a groundplate or platen 102.

The charged paper is exposed to a light image from a luminous imageprojector'104 of any known kind. The paper bearing the charge-image orlatent image in the form of an electrostatic charge then passes throughthe magnetic field or fields of the developer powder applying apparatusdescribed previously in detail. A guide plate 1% guides the paper web12' so that it is drawn through the magnetized zone at the proper leveland past a heater or fuser 108 where the developer powder is'melted andfused to the paper surface to form a permanent image.

Reference character 109 indicates an electric motor of any suitable kindor type which drives a feed roller 112. A pressure roller 116 serves topress the paper against the roller 112 so that it may be drawn throughthe several recording stages or stations described above.

The pulley 28 is driven by suitable means such as a motor 118. As shown,the pulley rotates on the shaft 25. The belt 36 is driven and passesover the pulley 27 which serves as the driven pulley. The pulley 23 isdriven for rotation in the opposite direction by a motor 119. beunderstood that the feed roller 112, the pulley 28 and the pulley 23 maybe driven from a single motor and any power transmission system known tothe art.

The ferromagnetic powder will be arranged in a bristle like array andform a continuous brush sweeping across the lower face of thephoto-conductive web. This lower face carries the latent charge image.The charge of the image will attract toner powder from the lowerpotential ferromagnetic bristles. The pigmented toner will color thecharge image so that, on the application of heat, a permanent picture ofthe image will be fused to the paper.

As the brush sweeps across the moving web, the supply of toner will besteadily depleted. As the belts move on to the downward rotating pulleys23 and the pulley (not shown) beside the pulley 27 and out of the highflux density region the toner depleted ferromagnetic powder will startdropping into the tray 40. When the belt leaves the pulley circumferenceto travel under the pole piece to the pick-up pulley it has passed outof the flux region and has shed all its ferromagnetic bristles. The tray4%) rotates on bearing 41, and may be turned by hand or be driven. Thetray 40 thus comprises a transporting means for the developer mix. Thepowder will therefore be carried from one pulley to the other. As thetray 4% rotates, a supply of toner powder is added to the mixture. Tonerpowder may be supplied from a hopper 5 having a spout 6 disposed todischarge toner powder onto the tray 46. This picking up and droppingoperation mixes the toner with the ferromagnetic carrier component sothat a uniform ratio mixture will be supplied to the brush.

Since the belts are made of a nonmagnetic material, a very thoroughdropping and reforming will occur. In brushes where the ferromagneticcarrier bristles are suspended from a magnetic substance like soft iron,which may retain a quantity of residual magnetism, the reformation ofthe brush may not be complete.

By nonmagnetic material. is meant herein. nonsferromagnetic materials.Paramagnetic and diamagnetic materials where the magnetic effect is veryslight are herein as a matter of convenience considered to benonmagnetic because they will function similar to nonmagnetic materialswhen used as conveyor belts to carry ferromagnetic bristle brushes ofthis type.

Since the pulleys 27 and 28 rotate in one direction, conveyor belt. 30will. rotate as shown. The conveyor It will.

belt 35 rotating on pulleys 23 and on the pulley beside the pulley 27will move across the web in the opposite direction. The concentration oftoner will be maximum as the brush first starts to move across the web.If there were only one conveyor moving across extremely wide sheets ofpaper such as large sheets of mechanical drawing, the coating on theside of the paper where the brush first contacts could possibly beheavier and darker than on the far side. By use of the twocounter-directed bristle conveyor belts or brushes, coloration will beof even darkness completely across the moving web with depletion in eachbrush counter-balancing the initial concentration in the other.

A closed fiux path is provided through pole piece to pole piece 17 tomagnets 20, to pole piece 18, to pole piece 11 and back to pole piece itthrough magnets 15 across the entire length of the belts. Equal lengthflux paths assure uniform flux distribution completely across the web.The moving brush, therefore, has bristles which are uniform in heightand stiffness at any point in its traverse of the web. Even brushingaction helps provide even coloration.

Brass plates 123 to 126 are provided on lower pole pieces 17 and 18 andbrass sides on plates 121, 122, 127 and 128 are provided on all of thepulleys to prevent the bristles from overlapping around the edges of thepole pieces and pulleys. Since the lines of flux do not travel throughthese brass pieces, the bristles cling only to the central portion ofthe belt over the iron leaving clean edges on the pulleys and polepieces and at the edges of the belts as stated above. Properconcentration of bristles toward the center of the pole pieces andpulleys is therefore provided. This prevents wasteful loss of toner overthe edges of the belt and pulleys.

Where a web of lesser width is fed through the developer brush, adeveloper brush which only has one of these endless conveyor beltbrushes might be utilized. In a short traverse the brush would not be sodepleted of toner in a single traverse at the end of its travel. Apractically even distribution of toner across the face of narrow webswill be achieved Without the necessity of having two such opposed movingbelts. With relatively narrow paper a magnetic flux return path aroundthe side of the paper would affect the uniformity in flux distributionto a lesser degree.

Another embodiment of the invention is illustrated in Figures 4 and 5.In this illustrative example a magnet 50 is placed above the paper 52while a pole piece 51 is located below the paper. The magnet 50 is of anelongated horse shoe shape and its polar edges are oppositely disposedwith respect to the elongated upstanding projections 161 and 162 of thepole piece 51. The pole piece 51 is suitably supported from anystationary part 163. The charged latent image is on the upper surface ofthe paper 52. Shafts 53 and 54 support sprocket wheels 55 and 56. Thesprocket wheels and shafts are made of a nonmagnetic material to preventattraction of the mix. The shafts are mounted in any suitable stationaryhearing (not shown). These sprocket wheels carry a flexible belt 60which may be of the type known as timing belt. Small iron pole pieces 61are fixed to the outer surface of the belt on by rivets s2. The shaft 53is rotated by a motor 63 through any suitable mechanical coupling device(not shown in detail). Shoes 57 and 58 of a suitable bearing metal suchas, for example, bronze are secured to the lower edges of the magnet.The pole pieces 51 are attracted by the magnet and slide against theseshoes. Circular trays 65 and 66 rotate with the sprocket wheels 55 and56 as the paper 52 carrying the latent charge image on its upper facemoves through the magnetic field. The paper 52 may be supported andmoved as described above. The belt moves across the paper in onedirection and then retraces its way across the paper in the oppositedirection. Ferromagnetic developer mix is suspended from the pole pieces61 on the belt and form a bristle-like array or brush of developer mixwhich sweeps across the surface of the paper.

The pole pieces will enter the magnetic field before they start to sweepacross the paper. This is accomplished by diagonally, shaping the ends171 and 172 of the magnet 50 and, correspondingly, the ends of the polepiece 51. A mixture of ferromagnetic component and toner powder heldtriboelectrlcally within the ferromagnetic mix is picked up by the polepieces 61 from the trays 55 and 56. It is picked up at regions 68 and 69W e the ieces 61 start to pass within the magnetic field existing in thegap between magnet 50 and pole pieces 51. The mixture is dropped at 7'3and 71 regions after the pole pieces leave the magnetic field in thegap. The magnets cover more of the trays on the pick up cycle than atthe drop points to assure that an adequate supply of developer mix ispicked up before the pole pieces 61'. start to sweep across the movingsurface of the paper.

The flux path will be continuous through the paper or web completelyacross the length of magnet 50 and pole piece 51 providing evendistribution of flux and even bristle formation completely across thesurface of the paper. Double belt counter-sweeping action is alsoprovided. Coloration of uniform texture even on very wide webs will beachieved by the uniform bristle formation as well as the compensatingdepletion of the counter-moving brushes.

On very narrow Webs a sweep type of brush with only one traversing beltmight be desired. if so, in either the nonmagnetic belt or ma netic beltembodiment one of the conveyor belt transverses might be eliminated orrouted away from the web surface and the respective brushless north andsouth poles of the magnet and pole piece brought extremely close to thesurface of the paper forming a very narrow gap through which the papermoves. This gap would be located in the direction to allow the paper tomove through the gap before it moves through the brush, such as forexample between pole pieces 11 and in Figure 2 or between the south poleof magnet 50 and end 162 on pole piece 51 in Figure 5. This prevents thegap from becoming clogged with bristles of ferromagnetic powder. Aperfectly uniform flux distribution across a single traversing conveyorwould be provided in this form of the invention.

The nonmagnetic belt type of moving brush illustrated in Figures 1, 2,and 3 might be equipped with two small rotating trays similar to theones in Figures 4- and 5. This would allow a more compact arrangementsince the tray it? might occupy a prohibitive amount of space.

What is claimed is:

l. Electrostatic printing apparatus comprising means for moving aphotoconductive web having a latent charge image imposed thereon along apredetermined path, an endless belt, means for supporting and drivingsaid belt whereby one run thereof traverses along a path at right anglesto the path of said web and with on run of said belt in close proximityto the charged surface of said web, a magnet structure for produ a manetic flux throughout the width of said Web and cngtnv of said belt, onerun of said belt being within said magnetic flux and the remaining runbeing outside of said magnetic flux, transporting means disposed incooperative relation with two regions of said one run of said belt, saidmagnet structure having an extension for developing a magnetic flux a.one of said regi for formation of a ferromagnetic developer mix into abristle-l array on said one run of said belt, supply means for saidtransporting means for adding developer powder to the ferromagnetic mixin makeup quantity, and means whereby in the other of said regi .5 saidferromagneg mix and unused developer power are released onto saidtransporting means for transport to said first mentioned region.

2. The combination set forth in claim 1 wherein the belt is comprised ofa nonmagnetic material.

3. The combination set forth in claim 1 wherein guide greater;

means -are providedifor said endlessbelt, saidguide meansdisposed fordireeting'said belt in its path across means located adjacent to onesurface of said web and substantially spanning the width thereof,magnetic pole means of polarity opposite to saidfirst pole means locatedadjacentto the opposite surface of said web substan tially spanningthewidth thereof forming together with said-liirst pole means a gap throughwhich'lines of 'flux emanating from one of said poles pass through theweb into the other of said poles, an endless conveyor a portion of whichis located between said poles traversing substantially the length ofsaid gap and passing across the moving surface of said-web carrying acharge of a latent image, ferromagnetic powder held to the surface ofthe conveyor adjacent said web formed in a bristle-lil e array extendingfrom said conveyor by said lines of flux, said bristles'tribo-electrically holding a quantity of pigmented eieotroscopicdeveloper powder, said bristles brushing continuously across the chargeof a latent image on the surface of said web whereby developer powder issupplied tor attraction to said latent image on said web.

5. The combination set forth in claim 4 wherein said endless conveyor iscomprised of nonmagnetic material.

6. A magnet structure for establishing throughout the width of a movingphotoconductive web of a continuous operating electrostatic printer auniform distribution of lines of magnetic flux comprising magnet meansfor providing said lines of magnetic flux, said magnet'means having oneportion disposed for creating in close proximity to'the surface of saidweb across the width of said web a relatively narrow region of onepolarity, said magnet means having a second portion disposed in closeproximity to said web creating a similar relatively narrow region ofpolarity opposite to that of said first region, said second region beingsubstantially parallel to said first region across the width of saidweb, return path means of magnetic material provided on the oppositeside of said web from said magnet means providing a conductive returnpath whereby lines of flux emanating from apole of said magnet meanswill pass through one of said pole regions on sai web into said returnpath means through said return path means through the other pole regionon said web back into the other pole of said magnet means.

' 7. In an electrostatic printing apparatus, means for supporting andmoving a photoconductive web bearing a latent electrostatic chargeimage, means for providing a developer powder applicator brush whichcontinuously sweeps over a photoconductive web supported and moved bysaid first named means comprising magnetic means for emanating lines offiux disposed in close proximity to said surface, said magnetic meanscreating narrow band regions of opposite polarity across said web, a;structure of magnetic material disposed adjacent to the opposite side ofsaid web from said magnetic means providing a path for lines of fluxemanating from one of said regions topass through the web into thestructure back through the web into another of said regions, an endlessconveyor means passing within said polar regions across the surface ofsaid web, means to provide a ferromagnetic developer mix to be formed ina bristle-like array extending-from said conveyor by said line of flux,said array brushing developer mix in intimate contact with the recordcarrying surface of said web.

8.'The combination set forth in claim, 7 wherein said endless conveyormeans is comprised of non-magnetic material,

9 -ln an electrostatic printer, means to support a sheet bearing an-Telectrostatic charge. image, means to: provide. a 'movingxbrushrofiferromagnetic powder arranged in. bristle-.likearray for traversingasheet supported by said.

sheet'supportingmeans, said second uamedmeanscom: prisinga magnet meansproviding a gap through which lines ofmagnetic fluxpass, a circulatingendlessbelt of: nonmagnetic materiaha: portion of said belt circuitbeing.

positioned within said gap, said sheet supporting means presenting saidsheet adjacent saidportion of said belt circuit, and means for supplyingferromagnetic powder to.-

a surface of. said belt at a region within said gap.

10; Means for providing a developer powder applicator. brush whichcontinuously sweeps the moving photoconductive web of an electrostaticprinter having a charge of a latent-image, imposed thereon comprisingmagnetic:

pole'means located-adjacent to one surface of said web and substantiallyspanning the width thereof, magnetic pole means of polarity opposite tosaid first pole means located adjacent to the opposite surface of saidwebsub- I stantiaily spanning the width thereof forming togetherwithsaidfirstpolemeansa gap through which'linesof.

flux emanating from one of said poles pass through the webinto the otherofsaid poles, an endless conveyor a portion of which is located betweensaid poles traversing. substantially the length of said gap and passingacross the moving surface of said web carrying a charge of a latentimage, ferromagnetic powder held to the surface of the conveyoradjacentsaid. web formed in a bristlelike array extending'from said conveyor bysaid lines of it flux,- said bristles tribo-electrically' holding aquantity of pigmented electroscopic developer powder, said bristlesbrushing continuously across the charge of a latent'image on the surfaceof said web whereby developer powder is supplied for. attraction to saidlatent image on said 1 web, and guide means for directing said conveyoracross said web in two separate oppositely directed traversals' acrosssaid web, a structure of magnetic material disposed-adjacentto theopposite side of said web from said magnetic means providing a path forlines of flux emanating from-one-of said regions to pass through the webinto the structure back through the web into another of saidregions, anendless conveyor means passing within said polar regions across thesurface of said Web, ferromagnetic developer mixformed in a bristle-likearray extending from said conveyor bysaid line of flux, said bristlesbrushing developer mix in intimate contact with the record carryingsurface of said web, and said con veyor passing across the web in onedirection within one of said narrow band polar regions and sweeping backacross the web in its return traverse within another of said narrowband, regions.

References Cited in the file of this patent 'UNITED STATES PATENTS573,485 Sanders et al. Dec. 22, 189.6 1,094,125 Cousins Apr. 21, 19141,140,642 Weingartner et al. May 25, 1916 1,828,958 Canton, Oct. 27,1931 2,239,970 Osborne Apr. 29, 1941 2,357,809 Carlson .a Sept. 12, 19442,591,121 Blind Apr. 1, 1952' 2,618,551 Walkup Nov. 18, 1952 2,624,652Carlson Jan. 6, 1953 2,705,199 Clark Mar. 29, 1955 FOREIGN BATENTS4455137 France Aug. 27; 1912'

1. ELECTROSTATIC PRINTING APPARATUE COMPRISING MEANS FOR MOVING A PHOTOCONDUCTIVE WEB HAVING A LATENT CHARGE IMAGE IMPOSED THEREON ALONG A PREDETERMINED PATH, AN ENDLESS BELT, MEANS FOR SUPPORTING AND DRIVING SAID BELT WHEREBY ONERUN THEREOF TRAVERSES ALONG A PATH AT RIGHT ANGLES TO THE PATH OF SAID WEB AND WITH ONE RUN OF SAID BELT IN CLOSE PROXIMITY TO THE CHARGED SURFACE OF SAID WEB, A MAGNET STRUCTURE FOR PRODUCING A MAGNETIC FLUX THROUGHOUT THE WIDTH OF SAID WEB AND LENGTHWISE OF SAID BELT, ONE RUN OF SAID BELT BEING WITHIN SAID MAGNETIC FLUX AND THE REMAINING RUN BEING OUTSIDE OF SAID MAGNETIC 